1. Field of the Invention
This invention relates to a method and a system to produce coolant and gases for a semiconductor fabrication facility, and more particularly to the use of a eat exchanger to transfer heat from water to liquid nitrogen in order to lower the temperature of the water and convert the liquid nitrogen to gaseous nitrogen for use in the semiconductor fabrication process.
2. Description of Related Art
FIG. 1 illustrates a typical layout of a semiconductor fabrication facility (cleanroom). The cleanroom includes areas for film growth, deposition, photolithography, etching, ion implantation, and photo-resist stripping. Processing equipment in the cleanroom includes CVD (chemical vapor deposition) systems, PVD (physical vapor deposition) systems, implanters, furnaces, RTP (rapid thermal processing (such as to anneal)) systems, etchers, plasma CVD systems, steppers, and SEMs (scanning electron microscopes). Typically, a substantial portion (for example, on the order of one-third) of the heat generated by process equipment is carried away by process-cooling water. Chillers are used to produce process-cooling water and they constitute about 18% of the total power consumption of a typical cleanroom according to xe2x80x9cULSI Technologyxe2x80x9d, edited by C. Y. Chang and S. M. Sze, published by McGraw-Hill Companies, Inc, 1996.
Process equipment also uses gaseous nitrogen as carrier gas, reactant gas, dopant, purge gas, and dilution gas in various semiconductor fabrication processes. Nitrogen can even be used to actuate pneumatics in semiconductor fabrication equipment. Typically, nitrogen is stored in tanks in its liquid state to conserve space. To convert the liquid nitrogen to gaseous nitrogen, the liquid nitrogen travels through a pipe with fins exposed to the atmosphere (e.g., a heat exchanger) so that the liquid nitrogen can absorb heat from the ambient conditions. Other gases used in semiconductor fabrication processes include oxygen and argon.
One problem with the prior art is that a separate chiller is provided to cool the coolant. This takes space and consumes power, thus adding to the cost of wafer fabrication. In addition, liquefied gas must be heated to become a gas, again, consuming power and thus adding cost to the fabrication process.
In accordance with one aspect of the invention, a cooling system includes a heat exchanger that supplies a coolant and a gas to one or more pieces of equipment used in a semiconductor manufacturing process. The heat exchanger is coupled to a source of coolant (e.g., water) and a source of liquid gas (e.g., liquid nitrogen) to transfer heat from the coolant to the liquid gas, thereby cooling the coolant and gasifying the liquid gas. The heat exchanger is coupled to supply the coolant and the gas to one or more units of semiconductor manufacturing equipment. Depending on the embodiment, the heat exchanger can supply the coolant and the gas to the same or different equipment.
In accordance with another aspect of the invention, a method for lowering the temperature of coolant (e.g., water) comprises supplying the coolant from a coolant supply to a heat exchanger, supplying a liquid gas (e.g., liquid nitrogen) from a liquid gas supply to the heat exchanger, and supplying the coolant from the heat exchanger to semiconductor fabrication equipment. The method may further include supplying the liquid gas in its gas state from the heat exchanger to the same semiconductor fabrication equipment or to different semiconductor fabrication equipment.
The present invention offers a substantial saving in the costs of semiconductor manufacturing. The coolant used in a semiconductor fabrication process is cooled with little or no use of chillers. Instead, the coolant is cooled using a liquid gas that must be converted to its gas state for use in the semiconductor fabrication process. Thus, energy consumption by the chillers is minimized and the cost of semiconductor manufacturing is reduced.